Copper(II) complexes of imidazolinone herbicides

Abstract

The copper(II) complexes formed by the imidazolinone herbicide Imazapyr or (±)-2-4-isopropyl-(4-methyl-5-oxo-2-imidazolin-2-yl)-nicotinic acid (H 2imz) are described. The compounds isolated in the solid state confirm that Imazapyr is a versatile bipy-like ligand able to chelate the metal ion through two different donor sets. The pair of pyridine and imidazole nitrogen atoms is bound to copper in [Cu(Himz) 3] and [Cu(Himz) 2(H 2O)]. In these, a five-coordination at the metal ion and a geometry close to the trigonal bipyramid are favoured. The weak carboxylate group does not play a primary role in the complex formation properties of Imazapyr. However, its involvement yields the polymetallic compounds [Cu(Himz) 2] and [Cu 3(Himz) 4(H 2O) 4](NO 3) 2. The deprotonation of the lactam group provides Imazapyr with a stronger donor set, the lactam and the pyridine nitrogens, yielding 1:1 polymeric complexes [Cu(imz)(H 2O)] and [Cu(imz)(H 2O) 3] · H 2O. With the methyl ester of Imazapyr (HimzOMe), the different charge of the ligand deprotonated at the lactam group allows a bis-chelated complex [Cu(imzOMe) 2(H 2O)] · H 2O in which the metal ion adopts a five-coordination. Analogies have been established between the complexes of H 2imz, HimzOMe and 2,2′-bipyridine.